US11060173B2 - Wrought processed magnesium-based alloy and method for producing same - Google Patents

Wrought processed magnesium-based alloy and method for producing same Download PDF

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US11060173B2
US11060173B2 US16/082,562 US201716082562A US11060173B2 US 11060173 B2 US11060173 B2 US 11060173B2 US 201716082562 A US201716082562 A US 201716082562A US 11060173 B2 US11060173 B2 US 11060173B2
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Hidetoshi Somekawa
Alok SHINGH
Tadanobu Inoue
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National Institute for Materials Science
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/06—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of magnesium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C23/00—Alloys based on magnesium

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  • the present invention relates to a wrought processed magnesium (Mg)-based alloy, and a method for producing the wrought processed Mg-based alloy. More specifically, the present invention relates to a wrought processed Mg-based alloy of fine grains, which is added by bismuth (Bi) and excellent in ductility at room temperature, and to a method for producing the wrought processed Mg-based alloy.
  • Mg wrought processed magnesium
  • Bi bismuth
  • an Mg alloy is attracting attention as a next-generation lightweight metal material.
  • an Mg metal crystal structure is a hexagonal crystal structure, therefore, the difference of critical resolved shear stress (CRSS) between the basal slip and the non-basal slip, i.e., the prismatic slip, is extremely large in the vicinity of room temperature. Accordingly, the Mg alloy has poor ductility as compared with other wrought processed metal materials of aluminum (Al), iron (Fe) or the like, therefore, the plastic deformation processing at room temperature is difficult.
  • CRSS critical resolved shear stress
  • Patent Literatures 1 and 2 the plastic deformability has been improved by the addition of rare earth elements including yttrium (Y), cerium (Ce), and lanthanum (La).
  • Y yttrium
  • Ce cerium
  • La lanthanum
  • the rare earth elements have a function of reducing the CRSS on non-basal, that is, a function of narrowing the gap of CRSS between the basal and the non-basal and facilitating the dislocation slip motion of non-basal.
  • the material price increases, therefore, from the economic point of view, it is required to improve the ductility and formability by the addition of cheaper conventional elements.
  • Non Patent Literature 1 introducing a large amount of grain boundaries (grain refinement) is effective for improving the ductility.
  • Patent Literature 3 a fine grain Mg alloy in which one kind of elements selected from the group consisting of Ca, Sr, Ba, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Dr, Tm, Yb, and Lu, each of which is a rare earth element or a general-purpose element, are contained in a minute amount; the grains are refined; and the strength properties are excellent has been disclosed. It is said that the increase in strength of this alloy is mainly attributed to segregation of these solute elements at grain boundaries. On the other hand, in the fine grain Mg alloy, the dislocation slip of non-basal is activated by the action of grain boundary compatibility stress.
  • any one of the additive elements also has a function of suppressing the development of grain boundary sliding, therefore, the grain boundary sliding substantially does not contribute to deformation. Accordingly, the ductility of these alloys at room temperature is required to be further improved at the same level as that of a conventional Mg alloy. That is, it is required to search for a solute element that does not suppress the development of grain boundary sliding while maintaining the microstructure on which grain boundary compatibility stress acts.
  • Patent Literature 4 an Mg alloy containing 0.07 to 2 mass % of Mn and having excellent ductility at room temperature.
  • Patent Literature 5 an Mg alloy that is excellent in ductility at room temperature can be obtained, even if Zr is contained in place of the Mn.
  • These alloys are characterized in that the average grain size is 10 ⁇ m or less, the elongation-to-failure is around 150%, and the m value being an index of the contribution of grain boundary sliding to deformation is 0.1 or more.
  • these alloys are characterized by using a stress reduction degree as an index of formability, and the value is 0.3 or more.
  • an object of the present invention is to provide a wrought processed Mg-based alloy, which is an Mg-based alloy in which a solute element that does not suppress the development of grain boundary sliding is added while maintaining the microstructure on which grain boundary compatibility stress acts, has excellent ductility at room temperature and secondary workability, and further is economically excellent as compared with a conventional Mg-based alloy to which a rare earth element or a general-purpose element is added.
  • the present inventors have found an idea of using Bi that has a large solid solution amount to Mg and has a low melting point, as a solute element. Moreover, the present inventors have found that by controlling the average grain size in a wrought processed Mg-based alloy to which Bi has been added alone, an effect that is at least equivalent to the effect of an Mg-based alloy to which Mn or Zr has been added alone and which has been proposed by the present inventors so far, can be obtained, and thus have completed the present invention.
  • Bi can be used as a solute element of an Mg-based alloy, for example, in Patent Literature 6.
  • Patent Literature 6 Bi is mentioned as one of the additional elements to be added to Mg that is a base material of an Mg alloy sheet material, and it is described that the amount be added is 0.001 to 5 mass %.
  • the Mg alloy sheet material of Patent Literature 6 is produced by positively imparting distortion to a rolled material, and it is said that heat treatment for the purpose of recrystallization is not performed before and after the step of imparting the distortion.
  • the present invention is characterized by the following.
  • a first aspect of the present invention is to provide a wrought processed Mg-based alloy having excellent ductility at room temperature, consisting of 0.25 mass % or more to 9 mass % or less of Bi, and a balance of Mg and inevitable components, in which an average grain size of an Mg parent phase after solution treatment and hot plastic working after casting is 20 ⁇ m or less.
  • a second aspect of the present invention is to provide the wrought processed Mg-based alloy described in the first aspect of the present invention, in which in at least one of the Mg parent phase and a grain boundary in a metal structure of the wrought processed Mg-based alloy, Mg—Bi intermetallic compound particles having a particle diameter of 0.5 ⁇ m or less are precipitated while mutually dispersing.
  • a third aspect of the present invention is to provide the wrought processed Mg-based alloy described in the first or second aspect of the present invention, in which a strain rate sensitivity exponent (m value) in a tensile test at room temperature or a compression test of the wrought processed Mg-based alloy shows 0.1 or more.
  • a fourth aspect of the present invention is to provide the wrought processed Mg-based alloy described in any one of the first to third aspects of the present invention, in which in a stress-strain curve obtained by a compression test of the wrought processed Mg-based alloy at room temperature, work hardening is not exhibited when a compressive strain is 0.2, a plateau region being in a state of constant stress exists, and breaking state is not generated.
  • a fifth aspect of the present invention is to provide the wrought processed Mg-based alloy described in any one of the first to fourth aspects of the present invention, in which a value of deformation anisotropy obtained by the tensile test at room temperature or the compression test of the wrought processed Mg-based alloy is 0.8 or more, and the wrought processed Mg-based alloy is capable of being deformed in an isotropic manner in three dimensions.
  • a sixth aspect of the present invention is to provide the wrought processed Mg-based alloy described in any one of the first to fifth aspects of the present invention, in which in an internal friction test by a nanoscale dynamic mechanical analysis method, a value of tan ⁇ at a frequency of 0.1 Hz is 1.2 times or more as compared with that of a pure magnesium material.
  • a seventh aspect of the present invention is to provide a method for producing the wrought processed Mg-based alloy described in any one of the first to sixth aspects of the present invention, in which an Mg-based alloy casting material passed through steps of melting and casting is subjected to solution treatment at a temperature of 400° C. or more to 650° C. or less for 0.5 hour or more to 48 hours or less, and then subjected to hot plastic working at a temperature of 50° C. or more to 550° C. or less and a cross section reduction rate of 70% or more.
  • An eighth aspect of the present invention is to provide the method for producing the wrought processed Mg-based alloy described in the seventh aspect of the present invention, in which the hot plastic working is any one of an extrusion processing, a forging processing, a rolling processing, and a drawing processing.
  • the content of Bi in an Mg-based alloy material for obtaining the effect of the present invention is 0.25 mass % or more to 9 mass % or less.
  • the distance corresponds to around three times the Burgers vector of Mg, and means a limit value at which lattice defects of dislocation or the like interact with each other in atomic bonding theory.
  • the size of an Mg—Bi intermetallic compound particle is preferably 0.5 ⁇ m or less, and more preferably 0.1 ⁇ m or less.
  • the average grain size of the Mg parent phase after hot plastic working is preferably 20 ⁇ m or less.
  • the average grain size is more preferably 10 ⁇ m or less, and furthermore preferably 5 ⁇ m or less.
  • the grain boundary compatibility stress generated in the vicinity of grain boundaries does not affect the whole area in grains. That is, it is difficult that the non-basal dislocation slip acts in the whole area in grains, and the ductility is not expected to be improved.
  • an Mg—Bi intermetallic compound having a size of 0.5 ⁇ m or less may be dispersed in the Mg grains and grain boundaries.
  • heat treatment such as strain relief annealing may be performed after hot plastic working.
  • the Bi element may be segregated or not be segregated at grain boundaries.
  • a smelted Mg—Bi alloy casting material is subjected to solution treatment at a temperature of 400° C. or more to 650° C. or less.
  • the solution treatment temperature is less than 400° C.
  • the solution treatment time is preferably 0.5 hour to 48 hours.
  • the solution treatment time is less than 0.5 hour, the diffusion of solute elements throughout the parent phase becomes insufficient, therefore, the segregation during casting remains, and a sound material cannot be created. In a case where it exceeds 48 hours, the operation time becomes long, and this is not preferred from an industrial point of view.
  • any method can be adopted as long as it can produce the Mg-based alloy casting material of the present invention, such as gravity casting, sand mold casting, die casting or the like.
  • the temperature for hot plastic working is preferably 50° C. or more to 550° C. or less. In a case where the processing temperature is less than 50° C., because the processing temperature is low, dynamic recrystallization is hardly generated, and a sound wrought processed material can be prepared. In a case where the processing temperature exceeds 550° C., recrystallization progresses during the processing, grain refinement is inhibited, and further this causes a reduction in the life of the mold in extrusion processing.
  • the total cross sectional reduction rate is 70% or more, preferably 80% or more, and more preferably 90% or more.
  • the strain application is not sufficient, therefore, the grain size cannot be refined.
  • an intermetallic compound including Mg—Bi is generated in the parent phase and in the grain boundaries before the strain application, that is, during the holding in a furnace or container heated to a predetermined temperature. In such a case, it is difficult to finely disperse these intermetallic compounds unless sufficient strain is applied.
  • hot plastic working method examples include extrusion, forging, rolling, and drawing, and any working method can be adopted as long as it is a plastic working method by which strain can be applied.
  • any working method can be adopted as long as it is a plastic working method by which strain can be applied.
  • the grain size of the Mg parent phase is coarse, therefore, the effect of the present invention cannot be obtained because.
  • index for evaluating the ductility and formability of the wrought processed Mg-based alloy at room temperature that is, the stress reduction degree and the strain rate sensitivity exponent (m value) will be described. Both of the indexes can be calculated from the nominal stress and nominal strain curve obtained by a tensile test.
  • the stress reduction degree can be determined by the following formula (1), and the value of the stress reduction degree is preferably 0.3 or more, and more preferably 0.4 or more.
  • ⁇ max is the maximum stress
  • ⁇ bk is stress at break, and an example of which is shown in FIG. 4 .
  • the presence or absence of grain boundary sliding along with deformation can be predicted by using an m value.
  • FIG. 1 a nominal stress-nominal strain curve obtained by a compression test of a typical extruded Mg-3 mass % Al-1 mass % Zn alloy at room temperature is shown. Although a yielding behavior is shown, it can be confirmed that a rapid stress increase, that is, work hardening occurs with the strain application. This work hardening is because twin crystals are formed during deformation and dislocations accumulate at the interface of these twin crystals.
  • the twin crystal interface is energetically unstable, which is different from a common grain boundary, therefore, in a case where dislocations accumulate excessively at the twin crystal interface, the twin crystal interface becomes a starting point of breakdown, that is, a starting point of crack formation. Accordingly, it is difficult to apply compressive strain of 20% or more. In order to improve the compressive deformability, it is required to suppress the formation of twin crystals and to develop the grain boundary sliding.
  • Plastic deformation of a common wrought processed Mg-based alloy is dislocation motion and deformed twin as described above.
  • the CRSS of both of the deformation mechanisms are greatly different, and the CRSS of the deformed twin is around half of the dislocation motion.
  • these deformation mechanisms is influenced by the stress application direction, and the dislocation motion preferentially acts in the tensile stress field, and the deformed twin preferentially acts in the compressive stress field. Therefore, in a common wrought processed Mg-based alloy, the deformation mechanism varies due to the stress application direction, and the deformation anisotropy is generated, that is, there is a problem that the deformation cannot be generated in an isotropic manner.
  • the grain boundary sliding is a sliding motion between grains, therefore, isotropic deformation in three dimensions is possible without being affected by the stress application direction.
  • (Deformation anisotropy) (Compression yield stress) ⁇ (Tensile yield stress) Formula (3)
  • the value of the deformation anisotropy of a common wrought processed Mg-based alloy is 0.5 to 0.6.
  • each yield stress is a value obtained by a tensile test and a compression test, and flow stress may be used.
  • the internal friction characteristics are excellent.
  • a dynamic viscoelasticity (nanoscale dynamic mechanical analysis) method that is one of the nano indentation methods may be used.
  • the value of tan ⁇ to the measurement frequency varies depending on the composition or production conditions of the wrought processed Mg-based alloy, the test conditions, or the like, and in the wrought processed Mg-based alloy according to the present invention, the value of tan ⁇ preferably shows a value of 1.2 times or more, more preferably 1.4 times or more, and furthermore preferably 1.5 times or more at a predetermined frequency as compared with a pure magnesium material having an average grain size almost the same as that of the wrought processed Mg-based alloy.
  • FIG. 1 shows a nominal stress-nominal strain curve obtained by a compression test of an extruded Mg-3 mass % Al-1 mass % Zn alloy at room temperature.
  • FIG. 2 shows a photograph of a microstructure of an extruded Mg—Bi alloy of Example 2 observed by a scanning electron microscope/electron back scattering diffraction.
  • FIG. 3 shows a photograph of a microstructure of an extruded Mg—Bi alloy of Example 3 observed by a scanning electron microscope/electron back scattering diffraction.
  • FIG. 4 shows a nominal stress-nominal strain curve obtained by a tensile test of an extruded Mg—Bi alloy of Example 2 at room temperature.
  • FIG. 5 shows a graph indicating a relationship between the flow stress and the strain rate of an extruded Mg—Bi alloy of each of Examples 1 to 3.
  • FIG. 6 shows a nominal stress-nominal strain curve obtained by a tensile test of an extruded Mg—Bi alloy of each of Examples 5 and 7 at room temperature.
  • FIG. 7 shows a photograph of a microstructure of an Mg—Bi alloy of Comparative Example 1 observed by an optical microscope.
  • FIG. 8 shows a nominal stress-nominal strain curve obtained by a compression test at room temperature.
  • FIG. 9 is a photograph of external view after compression test at room temperature.
  • FIG. 10 shows a nominal stress-nominal strain curve obtained by a compression test using a cylindrical test piece of an extruded Mg—Bi alloy of Example 3 at room temperature.
  • FIG. 11 shows a relationship between the frequency and the tan ⁇ , obtained by an internal friction test.
  • Bi and Mg were adjusted by using an iron crucible so that the target contents of Bi were 0.42 mass %, 2.50 mass %, 4.55 mass %, and 7.80 mass %, respectively, and the four types of Mg—Bi alloy casting materials were melted by using an iron crucible.
  • casting was performed by using an iron mold having a diameter of 50 mm and a height of 200 mm and by setting the melting temperature to 700° C. and the melting retention time to 5 minutes under an Ar atmosphere. After subjecting the casting material to solution treatment at 500° C. for 2 hours, the element concentrations of the Bi and the inevitable components were analyzed and evaluated by ICP emission spectroscopy. The results of the analysis are shown in Table 1.
  • Casting materials 1 to 4 after the solution treatment were processed into cylindrical extrusion billets each having a diameter of 40 mm and a length of 60 mm by machining.
  • the respective extruded Mg—Bi alloys were held in a muffle furnace set at 200 to 350° C. within a range of 24 hours or less to perform heat treatment.
  • Example 1 Mg-0.42Bi 110 None None 2.5 Example 2 Mg-2.5Bi 110 None None 0.9 Example 3 Mg-2.5Bi 140 None None 3 Example 4 Mg-2.5Bi 110 200 1 9.8 Example 5 Mg-4.55Bi 110 None None 2 Example 6 Mg-4.55Bi 110 200 1 8 Example 9 Mg-4.55Bi 110 350 1 13 Example 7 Mg-7.8Bi 110 None None 1.8 Example 8 Mg-7.8Bi 110 250 1 8 Example 10 Mg-7.8Bi 110 350 4 13 Comparative Mg-2.5Bi 140 350 3 21 Example 1 Comparative Mg-4.55Bi 110 350 2 21 Example 2 Comparative Mg-7.8Bi 110 350 6 21 Example 3
  • the microstructure observation of the prepared Mg—Bi alloy by extrusion was performed. Examples of the observed typical microstructure (the extruded Mg-2.5 mass % Bi alloys of Examples 2 and 3, respectively) are shown in FIGS. 2 and 3 . In both of the drawings, the area having the same contrast is one grain, and it can be understood that the average grain size of the extruded Mg-2.5 mass % Bi alloys is 20 ⁇ m or less even at different extrusion temperatures.
  • the average grain size of each of the Mg—Bi alloys was determined by a section method and summarized in Table 2.
  • it is important that the average grain size of the Mg—Bi alloy is 20 ⁇ m or less.
  • a tensile test was conducted at room temperature by setting the initial strain rate within the range of 1 ⁇ 10 ⁇ 2 s ⁇ 1 to 1 ⁇ 10 ⁇ 5 s ⁇ 1 .
  • a round bar test piece having a parallel part length of 10 mm and a parallel part diameter of 2.5 mm was used in accordance with the JIS standard. All of the test pieces were taken from a direction parallel to the extrusion direction.
  • FIG. 4 a nominal stress-nominal strain curve obtained by the tensile test at room temperature is shown.
  • the extruded Mg—Bi alloy of Example 2 had an elongation-to-failure of 165% and exhibited extremely excellent ductility even at a strain rate of 1 ⁇ 10 ⁇ 3 s ⁇ 1 .
  • the case where the stress rapidly decreased (20% in each measurement) is defined as a state of “breaking” (indicated as BK in the drawing), and the nominal strain at that time is summarized in Table 3 as elongation-to-failure.
  • the nominal stress and nominal strain curve of the extruded Mg—Bi alloy of Example 2 which is shown in FIG. 4 , indicates a large stress reduction degree after the maximum stress.
  • the value of ( ⁇ max ⁇ k)/ ⁇ max is 0.76, therefore, it is suggested that the plastic deformation limit of the alloy of the present invention is large, and the formability is excellent.
  • the value of the nominal stress at a nominal strain of 0.1 is taken as the flow stress, and the relationship between the flow stress and the strain rate is shown in FIG. 5 .
  • the slope of a straight line corresponds to the m value
  • the strain rates at which the tensile tests were performed are divided, and the values determined by a mean-square method are shown in Table 3.
  • the m values of the Mg—Bi alloy of Examples each indicate 0.1 or more, and due to the development of grain boundary sliding, high ductility is generated at room temperature.
  • the nominal stress-nominal strain curve obtained by a tensile test using each of the extruded Mg—Bi alloys of Examples 5 and 7 is shown in FIG. 6 .
  • the nominal stress of each of the extruded Mg—Bi alloys of Examples 5 and 7 greatly depends on the strain rate, and it is suggested that both of the extruded alloys have large m values.
  • the elongation-to-failure, the stress reduction degree, and the m value of each of the extruded alloys, which have been obtained by a tensile test are summarized in Table 3.
  • the forming ability was evaluated by a compression test at room temperature.
  • a tubular-type test piece having a tube wall thickness of 0.8 mm, a length of 17 mm, and an outer tube diameter of 7 mm was used, and the initial compressive strain rate was set to 1 ⁇ 10 ⁇ 3 s ⁇ 1 .
  • the test piece was collected from an extruded alloy in a direction parallel to the direction of the extruded alloy, and prepared by machining.
  • the obtained nominal stress-nominal strain curve is shown in FIG. 8 . it can be understood that the stress-strain curve of the Mg—Bi alloy is different from the aspect of the stress-strain curve of a common Mg-based alloy shown in FIG.
  • the Mg—Bi alloy does not exhibit work hardening, when the compressive strain is 0.2 after yielding, and further, even when the compressive strain is 0.5 or more, the stress is kept constant, and it can be confirmed that break has not been generated. This is because twin crystals are not formed during deformation, and grain boundary sliding is responsible for the deformation. Further, it can be understood that the dashed line area (denoted by P in the drawing) in FIG. 8 , that is, the plateau region corresponds to the deformability and exhibits excellent deformation properties.
  • the photograph of external view of the extruded Mg—Bi alloy after deformation is shown in FIG. 9 . It can be confirmed that there are no fissures, cracks, or the like on the surface and exhibits bellows deformation.
  • both of the alloys are different from the stress-strain curve of the Mg—Bi alloy, and have the same aspect as that of the common Mg-based alloy shown in FIG. 1 . That is, both of the Mg—Y alloy and the Mg—Al alloy exhibit large work hardening when the compressive strain exceeds at least 0.1 with the increase in strain application after yielding. This is because deformed twin is formed after yielding. Although the deformed twin and the parent phase interface have a function of inhibiting the dislocation motion, these stress concentration sites where dislocation has accumulated become the originating points of breakdown and cracks, therefore, it is conceivable to induce the early break.
  • the photograph of external view of the extruded Mg—Y alloy after deformation is as shown in FIG. 9 , and as compared with the extruded Mg—Bi alloy of Example 3 described above, the deformation amount is poor and the difference in the deformability is clear.
  • the stress-strain curve of the Mg—Bi alloy is different from the aspect of the stress-strain curve of a common Mg-based alloy shown in FIG. 1 .
  • the extruded Mg—Bi alloy did not exhibit work hardening after yielding, and even if the compressive strain was 0.5 or more, a rapid stress reduction did not occur, and the break did not occur.
  • the deformation stress is greatly affected by the strain rate, and is reduced with the decrease in the strain rate.
  • the deformed twin is responsible for the deformation, therefore, the deformation stress does not depend on the strain rate. Accordingly, in order to examine the deformation mechanism of an extruded Mg—Bi alloy during the compression test, as in the case of the tensile test, the m value between the strain rates is determined by using the nominal stress at a nominal strain of 0.1 as the flow stress. In Table 4, the m values at each strain rate are summarized. As shown in Tables 3 and 4, it can be understood that as in the case of the m value obtained by a tensile test, the m value is 0.1 or more, and the grain boundary sliding is responsible for the deformation also in the compression test.
  • each flow stress was set as the value of the nominal stress at the nominal strain of 0.1.
  • Table 4 The values of the deformation anisotropy are 0.9 or more irrespective of the amount of the Bi to be added or the average grain size.
  • the extruded Mg—Bi alloy is not affected by the deformation direction, and the material is capable of being deformed in an isotropic manner in three dimensions.
  • the value of deformation anisotropy becomes smaller, however, in the present invention, if the value of deformation anisotropy is 0.8 or more, it is determined that the material is capable of being deformed in an isotropic manner in three dimensions.
  • the values of the deformation anisotropy are 0.8 or more from the results of the above tensile tests at room temperature.
  • the internal friction characteristics were evaluated by a nanoscale dynamic mechanical analysis method installed in a nanoindentation device.
  • the frequency was set within the range of 0.1 to 100 Hz, a surface parallel to the extrusion direction was taken as the measurement surface, and 50 or more points were measured per condition.
  • the obtained relationship between the frequency and the tan ⁇ is shown in FIG. 11 .
  • the value of tan ⁇ decreased with the increase of the frequency, and it can be understood that the phenomenons are the same as one another irrespective of the amount of the Bi to be added. In this regard, the larger the value of tan ⁇ is, the more excellent the internal friction characteristics are.
  • the internal friction characteristics of a pure metal are excellent as compared with those of an alloy of the pure metal in many cases. This is because the interaction between the additional elements and the dislocation is activated by adding a solute element, and the dislocation motion and the grain boundary sliding, which are essential mechanisms for releasing the internal energy, are suppressed. Accordingly, as a comparative example, by using an extruded pure magnesium having an average grain size (3 ⁇ m) almost the same as that of the extruded Mg—Bi alloy, the internal friction characteristics were evaluated. The measuring instrument and measurement conditions were the same as those of the extruded Mg—Bi alloys of Examples 3, 5 and 7 as described above. In FIG.
  • the value of tan ⁇ was 0.043, but in contrast, in the extruded Mg—Bi alloys of Examples 3, 5 and 7, the values of tan ⁇ were 0.076, 0.073, and 0.065, respectively, and indicated at least 1.5 times or more, as compared with the value of tan ⁇ in the pure extruded magnesium. From these results, also it can be understood that the extruded Mg—Bi alloy of the present invention has more excellent internal friction characteristics than the pure metal has. The excellent internal friction characteristics of the Mg—Bi alloy are due to the activation of the grain boundary sliding.
  • the internal structure was refined by one time of hot plastic working, but in a case where the cross section reduction rate is smaller than the predetermined value, multiple times of hot plastic working may also be performed.
  • the Mg—Bi alloy of the present invention exhibits excellent ductility at room temperature, the Mg—Bi alloy is rich in secondary workability, is easy to be formed into a complicated shape including a plate shape, and further has isotropic deformability in three dimensions due to the deformation mechanism in which generation of deformed twin is suppressed because of the development of grain boundary sliding.
  • any break does not occur, even if large strain is applied, therefore, it can be said that the application as a shock absorbing material or a structural material to an automobile or the like can be achieved.
  • the grain boundary sliding since the grain boundary sliding is developed, the internal friction characteristics are excellent, and application to a part where vibration or noise is a problem can be considered.

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EP3653742A4 (en) 2017-07-10 2020-07-15 National Institute for Materials Science MAGNESIUM CORROYING ALLOY MATERIAL AND MANUFACTURING METHOD THEREOF
WO2019017307A1 (ja) 2017-07-18 2019-01-24 国立研究開発法人物質・材料研究機構 マグネシウム基合金展伸材及びその製造方法
CN109554645B (zh) * 2017-09-25 2021-04-13 中国宝武钢铁集团有限公司 一种室温超成形性镁或镁合金及其制造方法
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RU2716612C1 (ru) * 2019-07-29 2020-03-13 федеральное государственное бюджетное образовательное учреждение высшего образования "Тольяттинский государственный университет" Способ гибридной обработки магниевых сплавов
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